Manufacture of lubricating oils



MANUFACTURE OF LUBRICATING OILS William N. Axe, Bartlesville, kla.,assignor to Phillips Petroleum Company, a corporation of Delaware NoDrawing. Application January 16, 1952, Serial No. 266,789

8 Claims. (Cl. 196-18) This invention relates to the preparation oflubricating oils, particularly to those exhibiting low pour-points. Inone aspect this invention relates to the manufacture of Arctic oils, i.e. lubricating oils employed in internal combustion engines underextremely low atmospheric temperature conditions. In another aspect thisinvention relates to a process for solvent dewaxing an oil, employing anormally liquid ketone in conjunction with propane as an internalrefrigerant, which process has the internal refrigeration advantage ofpropane dewaxing, and the advantage of the narrow differential betweenchilling tem* perature and pour-point, characteristic of dewaxingprocesses employing a normally liquid dewaxing solvent. In still anotheraspect this invention relates to a method for dewaxing a partiallydewaxed oil, employing urea as a final dewaxing agent. In still anotheraspect this invention relates to a process for producing oils of verylow pour-point, e. g. Arcticoils, without the need for ex tremely lowsolvent dewaxing temperatures required here tofore. In one aspect thisinvention relates to the production of low pour-point oils from a waxcontaining lubrieating oil stock, dewaxing such a stock employing methylisobutyl ketone together with propane as an internal refrigerant, as adewaxing solvent, and then further de waxing a resulting partiallydewaxed and solvent-free oil, employing urea as the dewaxing agent.

In propane dewaxing of oils a solution of propane and a waxy oil ischilled, for example by vaporization. of a portion of the propane, tocause precipitation of the amount of wax necessary to impart the desiredpour-point to the recovered lubricating oil. The wax may be separatedfrom the propane-oil solution, for example by filtra tion or settling.The propane is vaporized fromthe oil for recovery of the finisheddewaxed oil. One undesirable feature of the propane dewaxing process isthe necessity for chilling the propane-oil solution to a temperaturewell below the desired pour-point of the finished oil. For example, itmay be necessary to chill a propane-oil solution to 40 F. to -60 F. inorder to dewax a lubricating oil to a pour-point of 0 This largedifferential between chilling temperature and pour-point of the dewaxedoil militates against the use of propane as a dewaxing solvent in theproduction of oils having low pour-point. The spread between chillingtemperature and pour-point is substantially unchanged for chillingtemperatures as low as -100 F. A second ditficulty of the propane'de'waxing process is the tendency of a propane-oil solution to supercoolwith the attendant inconvenience in having to induce crystallization ofthe wax.

In ordinary solvent dewaxing, the. oil is mixed with a normally liquidsolvent, for example methyl isobutyl ketone, and the mixture issubsequently chilled to a tem' perature at which suflicient waxprecipitates to yield an oil which, when separated from the precipitatedwax and the solvent, has the desired pour-point. The temperature towhich the solvent-oil solution must be cooled is ap' proximately thedesired pour-point temperature of the finished oil. Straight ketonedewaxing has the disadvantates Patent '0 tage of a lower heat transfercoetficient through the exchanger surface because of a wax layer, andhas the fur ther disadvantage that cooling to the dewaxing tempera turecannot be effected by evaporation of the solvent.

In accordance with my invention, I have provided for the manufacture oflow pour-point oils from wax-con taining lubricating oil stocks, bypartially dewaxing the said oil stock and then further dewaxing theresulting partially dewaxed oil, employing urea as a dewaxing agent. Thepartial dewaxing step is preferably effected employing as a dewaxingsolvent a normally liquid ketone in conjunction with propane as aninternal refrigerant, or if desired, employing a normally liquiddewaxing solvent, such as for example ketone-type solvents such asmethyl isobutyl ketone, acetone-benzol mixtures, estertype solvents suchas butyl acetate, amyl acetate or the like, and a blend of such acetateswith dichlorethyl ether,

and the like. Depending on the desired ultimate pourpoint of the oil tobe treated, the wax-containing oil stock can be treated with a normallyliquid ketone in con junction with propane as an internal refrigerant asa dewaxing solvent, without the added treatment with urea, although Ihave found that, when employing urea in this manner, pour-points of from10 to at least 20 F. lower are obtained, without the necessity ofemploying the low dewaxing temperatures ordinarily required whenproducing oils of comparably low pour-point by solvent de waxing. Myinvention is accordingly applied advantageously to the production ofArctic-type lubricating oils,- particularly when incorporatingpour-point depressant agents with the final low pour-point oil product.

In accordance with one embodiment of this invention, a lubricating oilcrude is distilled into a gas oil fraction, which is then distilled toproduce a distillate lube-oil base stock. This latter stock is thensolvent extracted employing a solvent such as for example phenol,furfural, or the like, from which extraction a solvent-freewax-containing ratfinate is recovered. The said rafiinate is then mixedwith a normally liquid ketone, preferably methyl isobutyl ketone,generally in a volume ratio to the ketone within the limits of 0.25:1 to1:1 although ratios outside this range are advantageously employed, asfor example as low as 0.20:1 or lower and up to about 4:1 or higher,together with liquid propane generally in a volume ratio of propane tothe ketone within the limits of 1:1 to 5:1. The desired dewaxingtemperature is effected by vaporizing propane in the resulting admixtureto provide the necessary chilling to that temperature. Chillingtemperatures can be at 0 F. to 60 F. dependent on the desired extent ofdewaxing. For preparation of low pourpoint oils this latter dewaxingtemperature may be within the limits of -20 to -40 F. or lower ifdesired. The resulting chilled oil admixture, contains precipitated waxand is filtered and the dewaxed oil is freed of solvent. The resultingdewaxed solvent-free oil has a pour-point generally from about --25 toabout --45 F., often from -30 to 40 F.

In accordance with another embodiment, a partially dewaxed oil, such asthe -25 to 45 F. pour-point oil above described, is treated by dewaxingwith urea as a dewaxing agent, whereby the pour-point is reduced by anadditional 10-20" F., without the necessity for employing a lowereddewaxing temperature. The temperature employed during the last saidtreatment, i. e. while employing urea as the dewaxing agent, is abovethe existing pour-point of the oil to be further treated, and can be ashigh as F. if desired. Preferred temperatures employed during treatmentwith urea, as described, are from about 0 F. to about 70 F. In carryingout this embodiment, the weight ratio of urea to the partially dewaxedoil being treated is generally from 0.1:1 to 321 room temperature.

In another embodiment, a wax containing raflinate as described above, asfor example recovered from phenol extraction, is partially dewaxedemploying a normally liquid dewaxing solvent followed by removal ofresulting precipitated wax and solvent from the oil, and treatment ofthe partially dewaxed. solvent-free oil with urea in the manner alreadydescribed to improve the pour-point of that oil, i. e. to lower it toform the desired low pourpoint oil.

Typical specifications of an Arctic oil are as follows: Viscosity at 210F. of 45 SUS (minimum) Viscosity at 40 F. of 39,500 SUS (maximum) Stablepour-point of 65 F.

Such oils have heretofore been prepared by blending substantialproportions of synthetic diester oils with a mineral oil base withsubsequent addition of viscosity index improvers and pour-pointdepressants.

In treating the partially dewaxed oil-with urea, higher temperatures,due to the instability of the urea-hydrocarbon complex, usually givelower yields while lower temperatures also give lower yields due tolower rates of reaction. To compensate for the lower rate of reaction atlower temperatures, it may be advisable to use an excess of urea inorder to increase the rate of formation of addition compounds, or toincrease the length of contact time, or both. For the production ofautomotive lubricants complete removal of the n-parafiins is notnecessary and usually is even undesirable, so reasonable rates ofcomplex formation are usually attainable by the use of an excess ofurea.

The presence of an activator increases the rate of ureahydrocarboncomplex formation to a marked degree. The amount of activator used mayvary over a relatively large range of concentration. However, excessiveamounts of activator should be avoided. The urea and the activator maybe added to the oil to be dewaxed as a saturated solution of urea inactivator, as an activator-urea slurry or as solid urea merely wet withthe activator. An excessive amount of activator is not desirable. Sincethe activators are solvents for urea, large amounts will decompose the"addition product by dissolving the urea. Materials which may be used assuch activators are such as methanol, ethanol, acetone, methyl ethylketone and low molecular weight ethers, such as dimethyl ether, diethylether, or methyl ethyl ether.

In carrying out one specific embodiment of this invention, the followingsequence of operations is employed in order to arrive at ana'lhpetroleum oil. (1') a solvent extracted raflinate derived from adistillate fraction segregated from the gas-oil fraction of alubricating oil crude is dewaxed to obtain a low pour-point oil bydissolving one volume of oil in from 1 to 5 volumes of methyl isobutylketone or other suitable dewaxing solvent and 1 to 2 volumes of propane.The oil-solvent mixture is chilled in a conventional propane dewaxingplant by internal refrigeration and filtered with continuous rotaryfilters. The solvent-free dewaxed oil will have a pour-point of -30 to50 F. depending on the filtration temperature. This compares. withpour-points of 0 to F. from conventional propane dewaxing. (2) Since itis necessary to produce a base stock with a pour-point well below -40F., the oil from step (1) is treated with urea in the presence of asuitable activator solvent system such as methanol or methyl-isobutylketone-water. Since the dewaxing in step 1) is non-selective, straightchain paraffins still remain in the oil and can be removed with urea atThis treatment will further lower the pour-point of the oil from to F.resulting in base stocks of -45 to -70 F. pour-point. Exhaustive ureatreatment of the original Waxy stocks can reduce the pourpoint only toabout -30 F. (3) The base stock from (2) is adjusted with respect toviscosity with a V. I. improver such as Acryloid 150 1 Polymerized cetylor lauryl methacrylate.

This invention is illustrated by way of the following examples:

EXAMPLE 1 Several wax-containing oil stocks were dewaxed to produce lowpour-point oils, employing methyl isobutyl ketone in conjunction withpropane as an internal refrigerant, as summarized in the followingtabulation (Table I).

Table I Fi1tra- Ketonol Propane] Wax Pour- Pour- Oil tion Oil, OilYield, Point Point Charge Temp, Volume (Cold), Wt. Dewaxed of Oil F.ratio Volume Percent Oil, (ll ialr ge,

1 Close cut Mid-Continent solvent extracted raflinate, 36.7 SUS 210.Mid-Continent solvent extracted rai'finate, SUS 210 F.

I Mid-Continent solvent extracted raflinate, 42 SUS 210 F.

Methyl lsohutyl ketone.

EXAMPLE II 375 pounds of a gas oil obtained from a Mid-Continent crudeoil was vacuum distilled to produce overhead distillate fractions l-l9,each roughly 4 volume per cent of the charge. Fractions 16-19 andbottoms product, recovered from the vacuum distillation arecharacterized by the following tabulated data (Table II).

Table [I Vol. Per- Viscosity Specific Fraction No. Weight, cent of at100 F., Gravity Lbs. Gas Oil SUS 60/60 F.

Charge These fractions (1.649 and bottoms) were blended to produce abase oil," as indicated in the following tabulation (Table III in acounter-current fiow extraction column. Extraction conditions employedand raifinate inspection data are tabulated as follows (Table IV).

Table IV OPERATING CONDITIONS Temperatures: F.)

Top column 182 Phenol outlet 185 Bottom separator 158 Oil inlet Waterinlet 102 Duration of run, hours 9.667

Feed rates: (gals/hr.)

Phenol at 140 F 3.515 Oil at 60 F 1.168 Water at 60 F 0.292 Total feed4.975

Phenol to oil ratio (volume) 3.01 Water to phenol ratio (volume) 0.083

INSPECTION em Rafiina-te oil:

Gravity, API 36.7 Specific gravity 60/60 F 0.8415 Viscosity at 100 F.,SUS 68.71 Viscosity at 210 F., SUS 36.51 Viscosity index, kinematic 112Viscosity gravity constant at 210 F 0.797 Refractive index at 70 C1.4450 Pour point, F 65 EXAMPLE HI Various samples of the rafiina-te oilof Table IV were partially dewaxed, employing methyl isobutyl ketone asa dewaxing solvent, in conjunction with propane as an internalrefrigerant. The resulting solvent-free partially dewaxed oil was thentreated with urea, i. e. urea-de- 1 Activator was 5 m1. of methanol pergram of oil. Urea to oil ratio was 2.0 by weight. Urea treatment waseffected with constant agitation at 70 F. for 1 hour.

2 Methyl isobutyl ketone.

3 Estimated.

EXAMPLE IV Two samples of the raflinate oil of Table IV, were partiallydewaxed employing methyl isobutyl ketone as a dewaxing solvent. Theresulting solvent-free partially dewaxed oil was then treated with urea,i. e. urea dewaxed. Data pertinent to these dewaxing steps are tabulatedas follows (Table VI).

Table VI Pour Pour Point Volumes of MIBK 1 Per Filtration Point of ofUrea Volume of Oil Tempera- Dewaxed Treated 1 ture, F. 011 Dewaxed 1Math 1 isobutyl ketone.

3 Aetlva tor was 5 m1. of methanol per gram 0! oil. Urea to oil ratio byweight was 2. Urea treatment efieeted with constant agitation at 70 F.for 1 hour.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure and the ap pended claims to the invention, theessence of which is a method for producing low pour-point oils, e. g.Arctic oils, by dewaxing a waxcon-taining oil, employing aketone-propane mixture, preferably methyl isobutyl ketone-propane,thereby providing a process having the internal refrigeration advantageof propane dewaxing and as a further advantage the narrow differentialbetween chilling temperature and the pour-point characteristic ofdewaxing processes employing normally liquid'solvents;

1 conjunction with propane as an internal refrigerant, so

as to provide a partially dewaxed oil, followed by further treating aresulting solvent-free dewaxed oil with urea at a temperature not lowerthan the pour-point of the oil treated and as high as P. if desired,thereby further reducing the pour-point by about l0-20 F. The lowpour-point oils of the process of this invention can be incorporatedwith selected pour-point depressants, when desired, and/or with selectedviscosity improvers.

I claim:

1. In a dewaxing process in which a lubricating oil stock is partiallydewaxed in a first dewaxing step and then the partially dewaxed oils isdewaxed in a second dewaxing step comprising admixing the partiallydewaxed oil with urea at a temperature in the range of 0 to 100 F. toform a precipitated urea-hydrocarbon complex, separating said complexfrom the last said admixture and recovering an oil having a lowpour-point, the improvement which comprises conducting said firstdewaxing step by forming an admixture of said lubricating oil stock withmethyl isobutyl ketone and with liquid propane, said admixture having avolume ratio of said oil stock to said ketone within the limits of0.20:1 to 1:1 and a volume ratio of said propane to said ketone withinthe limits of 1:1 to 5:1, chilling the resulting admixture to asubatmospheric temperature within the range of 0 to 60 F. by vaporizingpropane therefrom so as to thereby precipitate wax from the oilcomponent to partially dewax said oil, and separating the precipitatedwax from said admixture.

2. In a process for producing an Arctic-type oil comprising the steps ofsolvent extracting lubricating oil to remove naphthenic componentstherefrom in the extract, partially dewaxing the resultingwax-containing rafiinate in a first dewaxing step, and dewaxing theresulting partially dewaxed raflinate in a second dewaxing stepcomprising admixing the said partially dewaxed raffinate with urea in aweight ratio of 0.1:1 to 3:1, maintaining the last said admixture at atemperature in the range of 0 to 100 F. whereby urea forms a complexwith wax components in said raflinate contacted therewith, separatingsaid complex from the last said admixture, and recovering an Arctic oilhaving a low pour-point, the improvement which comprises conducting saidfirst dewaxing step by forming an admixture of said wax-containingraffinate with methyl isobutyl ketone and with liquid propane, saidadmixture having a volume ratio of said oil stock to said ketone withinthe limits of 0.20:1 to 1:1 and a volume ratio of said propane to saidketone within the limits of 1:1 to 5 :1, chilling the resultingadmixture to a subatmospheric temperature within the range of 0 to 60 F.by vaporizing propane therefrom so as to thereby precipitate wax fromthe oil component to partially dewax said oil, and separating theprecipitated wax from said admixture.

3. The process of claim 2 wherein a liquid activator is employed inconjunction with said urea to increase the rate of urea-hydrocarboncomplex formation.

4. The process of claim 3 wherein said activator contains said urea insolution therewith.

5. The process of claim 3 wherein said urea is initially associated withsaid activator as an activator-urea slurry.

6. The process of claim 3 wherein said urea is wet with said activator.

7. The process of claim 2 wherein, subsequent to separating the saidcomplex from the said admixture containing same, a pour point depressantis added to the said oil in an amount sufiicient to further reduce thepour point of said oil.

8. The process of claim 2 wherein, subsequent to separating the saidcomplex from said admixture containing same, a viscosity improvementagent is added to the said oil in an amount suflicient to furtherdecreas ethe viscosity References Cited in the file of this patentUNITED STATES PATENTS Bahlke Oct. 15, 1935 Winning et a1. -I. Tune 30,1936 Sacra Oct. 6, 1953

1. IN A DEWAXING PROCESS IN WHICH A LUBRICATING OIL STOCK IS PARTIALLYDEWAXED IN A FIRST DEWAXING STEP AND THEN THE PARTIALLY DEWAXED OILS ISDEWAXED IN A SECOND DEWAXING GROUP COMPRISING ADMIXING THE PARTIALLYDEWAXED OIL WITH UREA AT A TEMPERATURE IN THE RANGE OF 0 TO 100*F. TOFORM A PRECIPITATED UREA-HYDROCARBON COMPLEX, SEPARATING SAID COMPLEXFROM THE LAST SAID ADMIXTURE AND RECOVERING AN OIL HAVING A LOWPOUR-POINT , THE IMPROVEMENT WHICH COMPRISES CONDUCTING SAID FIRSTDEWAXING STEP BY FORMING AN ADMIXTURE OF SAID LUBRICATING OIL STOCK WITHMETHYL ISOBUTYL KETONE AND WITH LIQUID PROPANE, SAID ADMIXTURE HAVING AVOLUME RATIO OF SAID OIL STOCK TO SAID KETONE WITHIN THE LIMITS OF0.20:1 TO 1:1 AND A VOLUME RATIO OF SAID PROPANE TO SAID KETONE WITHINTHE LIMITS OF 1:1 TO 5:1, CHILLING THE RESULTING ADMIXTURE TO ASUBATMOSPHERIC TEMPERATURE WITHIN THE RANGE OF 0 TO -60* F. BYVAPORIZING PROPANE THEREFROM SO AS TO THEREBY PRECIPITATE WAX FROM THEOIL COMPONENT TO PARTIALLY DEWAX SAID OIL, AND SEPARATING THEPRECIPITATED WAX FROM SAID ADMIXTURE.